Hard Disk Drive (HDD)

Hard disk drives are mass storage devices. It is used to store large amount of data and information which can be accessed easily. The hard drive is where your programs are installed and where you save information on your computer. Lots of storage space means that you can have a wide variety of different software. The first hard disk drives were small in capacity, physically large, and expensive when compared to the cost of drives today. They were about 4 inches tall, 5.25 inches wide, and 8 inches long, and they weighed almost 10 pounds. In 1981, IBM introduced the XT computer with a 10-MB hard drive, and new owners wondered what they would do with all that space. Today, a new hard disk drive can fit in your pocket and hold over 17 GB of data. In this lesson, we examine hard disk drives, from the early versions to today's mini-monsters

When installing two hard drives, it is necessary to check the jumper setting for the Master/Slave configuration. The jumper pins for Master/Slave can be found between the power connector and IDE ribbon cable connector. Every hard drive manufacturer has different pin configurations which is found on the information pasted in the hard drive itself

• Master is used for the first hard drive
• Slave is for the second hard drive.

Physical Characteristics

The first form of PC mass storage was the magnetic tape drive, basically the same as a music cassette recorder. Even thought the tape has been prove as a good medium for storing large amount of data, it had some significant limitations. It is easily damage, the data was slow due to the way data is organized on tape. By providing random access (the ability to go directly to any point on the data surface), floppy disks are a major improvement, but they are too slow and too limited in capacity for modern applications. The original concept behind the hard disk drive was to provide a storage medium that held large amounts of data and allowed fast (random) access to that data. Data on a hard drive can be accessed directly, without requiring the user to start at the beginning and read everything until finding the data sought. Hard disk drives are composed of several platters, matched to a collection of R/W heads and an actuator. Unlike floppy disk drives, a hard disk drive assembly is housed in a sealed case, which prevents contamination from the surrounding environment. Each case has a tiny aperture with an air filter. This allows the air pressure to be equalized between the interior and the exterior of the drive.

The platters are often made of an aluminum alloy and have a thin magnetic- media coating on both sides. After coating, the platters are polished and given another thin coating of graphite for protection against mechanical damage caused by physical contact between the data heads and the platter surface. The R/W heads "float on a cushion of air" above the platters, which spin at 3500 to 12,000 revolutions per minute (rpm). The distance (flying height) between the heads and the disk surface is less than the thickness of a fingerprint.

Hard disks are organized as a concentric stack of platters. The data is stored on concentric circles on the surfaces known as tracks. Sections within each track are called sectors. A sector is the smallest physical storage unit on a disk and typically it will hold 512 bytes of data. The disk itself can't handle smaller amounts of data than one sector. As the platters spin, the drive heads move in toward the center surface and out toward the edge. In this way, the drive heads can reach the entire surface of each platter. Reading from 2 tracks implies a realignment of the reading heads, thus it takes longer than reading a single track.

Hard Disk Basics

-The first IBM hard disk drives came out in the late 1970s and early 1980s and were code-named "Winchester." The original design concept included two 30-MB units in one enclosure: 30-30 (hence Winchester, after the well-known rifle cartridge popular in western movies). The PC-XT was the first personal computer to include a hard disk. They were called fixed disks because they were not removable by the end user, like a floppy. (Old mainframe computers had hard platters that were removable by a trained technician.) The Winchester technology is the forerunner of all PC fixed disks. - hard disks use a technology called magnetic recording scheme in writing a data, same is true with cassette tapes. In a hard disk, the read/write head "flies" over the disk, never actually touching it.

NOTE: For more information and clarification with regard on this topics, feel free to read “A+ Certification Training Kit / Microsoft Corporation.--3rd Ed.” PUBLISHED BYMicrosoft PressA Division of Microsoft CorporationOne Microsoft WayRedmond, Washington 98052-6399 Copyright © 2001 by Microsoft Corporation